Preparation of β-alaninediacetic acid or its alkali metal or ammonium salts

ABSTRACT

β-Alaninediacetic acid (Ia) or its alkali metal or ammonium salts (Ib) are prepared by a process in which iminodiacetic acid and acrylic acid 
     a) for the preparation of Ia, are reacted with one another in a nonbasic aqueous medium and 
     b) for the preparation of Ib, are reacted with one another in an alkaline aqueous medium or an aqueous medium containing a nitrogen base, or the Ia formed in the nonbasic medium is converted with an alkali metal base, ammonia or an amine into Ib.

This is a division of application Ser. No. 07/394,816, filed on Aug. 17,1989, now U.S. Pat. No. 5,068,416.

The present invention relates to a novel process for the preparation ofβ-alaninediacetic acid (Ia) or its alkali metal or ammonium salts (Ib).

Like nitrilotriacetic acid or ethylenediaminetetraacetic acid or thesalts of these aminopolycarboxylic acids, the compounds la and Ib areimportant complexing agents.

It is known that β-alaninediacetic acid can be prepared by preparingchloroacetic acid with β-alanine (G. Schwarzenbach et al., Helv. Chim.Acta 32 (1949), 1184). The cyanomethylation of β-alanine toβ-alanine-diacetonitrile (V. G. Yashunskii et al., Zh. Vses. Khim.Obschestva im. D.I. Mendeleeva 10 (1965), 105) and the reaction ofiminodiacetic acid with acrylamide to give β-alanine-N,N-diacetic acidmonoamide (DE-A 27 27 755) have also been disclosed.

The two first-mentioned processes require β-alanine as a startingmaterial, which is relatively difficult to obtain, and necessitate aplurality of process stages, while the addition reaction ofiminodiacetic acid, which is readily obtainable from ammonia,hydrocyanic acid and formaldehyde, with acrylamide, and thecyanomethylation of β-alanine, give only one derivative ofβ-alaninediacetic acid, from which the acid is obtained only bysubsequent hydrolysis of the cyano group or of the amide group.

It is an object of the present invention to make the title compounds Iaand Ib more readily obtainable than in the past.

We have found that this object is achieved by a process for thepreparation of β-alaninediacetic acid (Ia) or its alkali metal orammonium salts (Ib), wherein iminodiacetic acid and acrylic acid

a) for the preparation of Ia, are reacted with one another in a nonbasicaqueous medium and

b) for the preparation of Ib, are reacted with one another in analkaline aqueous medium or an aqueous medium containing a nitrogen base,or the Ia formed in the nonbasic medium is converted with an alkalimetal base, ammonia or an amine into Ib: ##STR1##

Advantageously, equimolar amounts of acrylic acid and iminodiacetic acidare used. The organic acids are used in an amount of, in general, 20 to50, preferably from 30 to 40, % by weight, based on the total aqueousmixture. The reaction begins noticeably at 20° C. and usually takes from2 to 20 hours at from 60° to 100° C.

To achieve a shorter reaction time, the reaction may be carried out athigher temperatures of up to 200° C. in an autoclave.

The temperature range of from 70° to 100° C. is preferred for reasonsrelating to application. By adding small amounts of organic or inorganicacids, such as formic acid, acetic acid, hydrochloric acid or sulfuricacid, the reaction rate can be increased. Ia is preferably prepared at apH of from 0 to 1.

When the reaction is complete, the crystalline acid can be isolated fromthe aqueous solution by a conventional method.

Advantageously, up to 50% of the water are first removed from thereaction mixture under reduced pressure. The residue is thenadvantageously cooled to 0°-5° C., and the β-alaninediacetic acid can becrystallized out, filtered off and washed with ice water in amounts ofup to 50% of the amount of water used as a solvent for the reaction ofthe iminodiacetic acid with acrylic acid. The product is obtained in apurity of from 97 to 99.5% by weight and in yields of from 95 to 98.5%.

Aminopolycarboxylic acids very generally have a low water solubility,and it is for this reason that in many cases their alkali metal orammonium salts, which are more readily soluble in water, are preferablyused.

The-corresponding salts of β-alaninediacetic acid (Ib) in which all,three acid functions are neutralized are directly obtainable byembodiment (b) when the novel process is carried out in a neutral basicmedium, advantageously at a pH of from 7 to 9, and an alkali metalhydroxide, ammonia or an organic amine is added as the neutralizingbase.

Sodium hydroxide solution is preferably used, but it is also possible toemploy other basic compounds, such as sodium carbonate, sodiumbicarbonate, potassium hydroxide, potassium carbonate or ammonia. Othersalt-forming bases which may be used are primary, secondary or tertiaryaliphatic organic amines where the aliphatic radicals are of 1 to 4carbon atoms, for example methylamine, dimethylamine or trimethylamine.The other reaction conditions in the case of embodiment (b) are the sameas those in procedure (a). The acids Ia can of course also be convertedsubsequently into their salts Ib in a conventional manner.

The novel process can be carried out both batchwise and continuously andpermits the large-scale industrial production of β-alaninediacetic acidor its alkali metal or ammonium salts in a simple manner in high yieldsand high purity.

EXAMPLE 1

A stirred mixture of 36 g (0.5 mole) of acrylic acid, 66.5 g (0.5 mole)of iminodiacetic acid, 130 ml of water and 20 ml of anhydrous aceticacid was kept at 100° C. for 3 hours.

After the mixture had been cooled to room temperature, 50 ml of waterand acetic acid were removed under reduced pressure (0.02 atm). Thereaction mixture was then cooled to 5° C., after which the productprecipitated in crystalline form was filtered off and washed with 60 mlof ice water.

Yield: 100.5 g (0.49 mole) of β-alaninediacetic acid=98.5%.

Purity: 99.5% by weight.

EXAMPLE 2

A mixture of 267 g (2.0 moles) of iminodiacetic acid and 500. ml ofwater was neutralized with 50% strength by weight NaOH to pH 7.

144 g (2.0 moles) of acrylic acid were the added dropwise in the courseof 30 minutes while stirring, the pH of the mixture being kept at 7-8 bysynchronous addition of 50% strength by weight NaOH. The reactionmixture was then stirred for 12 hours at 70° C. 250 ml of water werethen removed under reduced pressure (0.02 atm). The mixture was thencooled to 0° C., after which the product precipitated in crystallineform was filtered off and washed with 150 ml of ice water.

Yield: 525 g (1.94 moles) of the trisodium salt of β-alaninediaceticacid=97%.

Purity: 99.2% by weight.

We claim:
 1. A process for the preparation of an alkali metal salt ofβ-alaninediacetic acid comprising:reacting iminodiacetic acid andacrylic acid in an aqueous medium containing sodium hydroxide, sodiumcarbonate, sodium bicarbonate, potassium hydroxide or potassiumcarbonate to form said alkali metal salt of β-alaninediacetic acid, saidaqueous medium having a pH of 7 to
 9. 2. A process for the preparationof an ammonium salt of β-alaninediacetic acid comprising:reactingiminodiacetic acid and acrylic acid in an aqueous medium containingammonia or an organic amine, said aqueous medium having a pH of 7 to 9,said organic amine being a primary, secondary or tertiary aliphaticamine wherein said aliphatic group is of 1 to 4 carbon atoms.
 3. Theprocess of claim 1, wherein said reaction is carried out at from 70° to100° C.
 4. The process of claim 2, wherein said reaction is carried outat from 70° to 100° C.